Statistical comparison of the antibacterial activities of broad-spectrum penicillins against gram-negative bacilli

Piperacillin 2 g/tazobactam 0.5 g is as effective as imipenem 0.5 g/cilastatin 0.5 g for the treatment of acute uncomplicated pyelonephritis and complicated urinary tract infections

This randomised, double-blind, multicentre trial compared piperacillin/tazobactam (2 g/0.5 g/q8h) and imipenem/cilastatin (0.5 g/0.5 g/q8h) as monotherapy in patients with acute pyelonephritis or complicated urinary tract infections. In total, 237 patients were randomised to receive either piperacillin/tazobactam (n=161) or imipenem/cilastatin (n=166). At the early follow-up (=test-of-cure-visit) 5-9 days after antibiotic therapy, clinical success was noted in 122/147 (83.0%) piperacillin/tazobactam recipients compared with 123/154 (79.9%) imipenem/cilastatin recipients, thus proving that both treatments were equally effective. On a descriptive level, an advantage of piperacillin/tazobactam was demonstrated. Microbiological success at the early follow-up was 78/135 (57.8%) for piperacillin/tazobactam and 70/144 (48.6%) for imipenem/cilastatin. These results were confirmed by equivalent success rates on the last therapy day. Both drugs were generally well tolerated.

In vitro activities of quinolones, beta-lactams, tobramycin, and trimethoprim-sulfamethoxazole against nonfermentative gram-negative bacilli

From 1991 to 1995, 8,975 nonfermentative gram-negative bacilli were isolated from patients at The Ohio State University Medical Center: 71% Pseudomonas aeruginosa, 14% Stenotrophomonas maltophilia, 7.6% Acinetobacter baumannii, and < 2% each of 25 other species. The MICs of trovafloxacin (CP-99,219), ciprofloxacin, ofloxacin, ampicillin-sulbactam, piperacillin, piperacillin-tazobactam, ceftazidime, cefoperazone, ceftriaxone, imipenem, tobramycin, and trimethoprim-sulfamethoxazole (TMP-SMZ) were determined for 308 isolates, representing 13 species, by a standardized broth microdilution method. The activities of all drugs were species dependent. The fluoroquinolones had inconsistent activity against most species, although several relatively uncommon nonfermenters were consistently susceptible or resistant. Trovafloxacin was considerably more active than ciprofloxacin and ofloxacin against S. maltophilia, A. baumannii, and several less common species. Among the beta-lactams, relative activities varied considerably; overall, imipenem had the broadest spectrum of activity but was inactive against S. maltophilia and Burkholderia cepacia isolates. Tobramycin and TMP-SMZ had stereotypic spectra of activity. Tobramycin was active against most species except S. maltophilia, Alcaligenes xylosoxidans subsp. xylosoxidans, Burkholderia spp., and Weeksella virosa. TMP-SMZ was active against most species except P. aeruginosa and Pseudomonas fluorescens-putida. A review of laboratory records indicated few changes in susceptibility patterns from 1991 to 1995; the only clear trend was toward increasing P. aeruginosa resistance to all classes of drugs.

Antibiotics in the treatment of wounds

In selecting an antibiotic, considerations include the sensitivity of the pathogen, drug distribution to the site of infection, bacteriostatic or bactericidal action under the existing tissue conditions, safety, and cost. Ideally, in vitro susceptibility of the pathogen can be obtained. In addition, cytologic evaluation, including a Gram stain, may be helpful in directing the initial course of therapy. Antibiotic sensitivity does not by itself guarantee satisfactory results. The terms "sensitive" and "resistant" are relative terms based on achievable blood levels of antimicrobial agents. The term "sensitive" implies that the level necessary to inhibit bacterial growth is achieved when an adequate dose is given at appropriate intervals. The distribution of the drug and, in turn, the level achieved at the site of infection depends on a number of factors, including molecular size, protein binding, and lipid solubility. Because, in most cases, specific tissue concentrations are not known, serum concentrations are used to represent the levels in the extracellular fluid space, which is the site of most bacterial infections. The local environment can further enhance or hinder antimicrobial penetration and activity. The antibiotic concentration achieved in the blood affects the concentration at the site of infection because simple passive diffusion appears to be the method of transport for most antibiotics. The antibiotic activity after reaching the site of infection is influenced by environmental conditions. Local production of enzymes, purulent and fibrinous exudate, and pH changes can adversely affect drug action. With many of these variables being difficult to predict, knowledge of etiologic agents is the cornerstone of rational use of the antimicrobial drugs. A reasonable suspicion based on clinical signs and knowledge of likely pathogens can guide the initial choice of antimicrobial therapy. Since both aerobic and anaerobic organisms may be involved in wound infections, and because antibiotic sensitivity of many of these pathogens is unpredictable, broad-spectrum antimicrobial therapy is often warranted initially.

Therapeutic evaluation of piperacillin for acute pulmonary exacerbations in cystic fibrosis

The efficacy and pharmacokinetics of piperacillin monotherapy were studied in 46 patients with cystic fibrosis. Two patients were dropped from the study within 24 hr of enrollment because of drug-associated nausea and vomiting. Initially fourteen older patients (greater than 12 years) receiving piperacillin 450 mg/kg/day underwent a preliminary evaluation. Based on the results, 30 younger patients (less than or equal to 12 years) randomized in a double-blind fashion received either 600 or 900 mg/kg/day of piperacillin in six divided doses. Pharmacokinetic parameter estimates for t1/2 Vdss, and Cl were similar for first dose and steady-state evaluations. In 27 patients, approximately 43% of the administered dose was recovered in the urine after 4 hr. Piperacillin CiR averaged 49% of the total Cl. No difference in overall clinical efficacy could be identified between 600 and 900 mg/kg/day of piperacillin using two different objective scoring systems. Although a reduction in sputum Pseudomonas colony counts was greater following the 900 mg/kg/day regimen, this appeared to be independent of clinical effect. In 14 patients (32%), a distinct adverse serum-sicknesslike reaction was observed. The incidence of this reaction appeared to increase as the dose of piperacillin increased. All signs and symptoms of this reaction resolved within 36 hr of discontinuing piperacillin administration but recurred immediately on rechallenge in four patients. All patients with the adverse reaction were subsequently treated with beta-lactam antibodies without ill effect. Overall, clinical improvement appeared to be independent of the piperacillin dose. Our data support the use of total daily piperacillin dosages not exceeding 600 mg/kg.

Comparative in vitro activities of apalcillin and piperacillin against gram-negative bacilli

The susceptibilities of 317 gram-negative bacilli to apalcillin and piperacillin were determined by standardized microdilution and disk diffusion tests. The respective percentages of strains susceptible to less than or equal to 64 micrograms of apalcillin and piperacillin per ml were as follows: members of the family Enterobacteriaceae, 90 and 88%; randomly selected Pseudomonas aeruginosa, 100 and 100%; multi-drug-resistant P. aeruginosa, 100 and 75%; and other nonfermenters and Aeromonas hydrophila, 99 and 97%. The drugs had equal activity against Enterobacteriaceae and A. hydrophila; apalcillin was more active against Pseudomonas species and Acinetobacter calcoaceticus, and piperacillin was more active against other nonfermenters. By using linear regression analysis, we found that the MICs of apalcillin and piperacillin were highly interrelated; the lines of best fit had slopes close to unity, and correlation coefficients (r) were greater than 0.90 for Enterobacteriaceae as a group and for other species individually. With disk diffusion testing, inhibition zone diameters around 100 micrograms apalcillin and 100 micrograms piperacillin disks correlated well with respective MICs for Enterobacteriaceae and P. aeruginosa (r = -0.93 to -0.96). Using an error rate-bound classification scheme, we determined breakpoints for apalcillin susceptibility and confirmed those previously established for piperacillin to be appropriate. The apalcillin disk, with modified breakpoints, could be used to predict piperacillin MICs for all organisms, but the piperacillin disk could not be used to predict apalcillin MICs for nonfermenters.

Piperacillin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Piperacillin is one of the new generation of semisynthetic penicillins which can be administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria. Although piperacillin has shown greater activity against beta-lactamase-producing organisms than the other penicillins, it is hydrolysed by the plasmid-mediated beta-lactamases (TEM-1). Activity against Pseudomonas aeruginosa is better than that of ticarcillin, carbenicillin and mezlocillin. Although only limited controlled studies have been reported, in those which have been conducted and in a larger number of open studies piperacillin was effective in the treatment of complicated urinary tract infections and lower respiratory tract infections, particularly pneumonia, caused by Gram-negative bacilli. Favourable clinical results have been obtained in patients with infections caused by mixed aerobic/anaerobic organisms (such as intra-abdominal infections) but the relatively average in vitro activity of piperacillin against Bacteroides fragilis may not indicate its usage in situations where this organism is the suspected or proven pathogen. Piperacillin in combination with an aminoglycoside or a 'third generation' cephalosporin gave encouraging results in the treatment of infections in immunocompromised patients, whilst its penetration into the diseased central nervous system and lack of toxicity indicate a potential value in the treatment of neonatal Gram-negative bacillary meningitis, particularly where the causative organism is Pseudomonas aeruginosa. Whether piperacillin alone is appropriate therapy for conditions usually treated with aminoglycosides (other than pseudomonal infections) needs additional clarification, but if established as equally effective in such conditions it has the advantages of its apparent lack of serious adverse effects and freedom from the need to undertake plasma concentration monitoring. These advantages would not, however, apply when considering one of the new (third generation) cephalosporins as alternative therapy in non-pseudomonal infections. Generally, however, it is still considered necessary to treat serious and complicated infections with combination therapy, either a cephalosporin, or in cases of resistance to P. aeruginosa an aminoglycoside.